Circuit interrupter



June 23, 1970 Filed July 24, 1968 TUTOMU HANAFUSA CIRCUIT INTERRUPTER '7 Sheets-Sheet 1 TUTOMU HANAFUSA ggf/5M 1 y ArroRNEYs June 23, 1970 TUTOMU HANAFUSA 3,517,355

CIRCUIT INTERRUPTER Filed July 24, 1968 7 shetsfsneet z INVENTOR TUTOMU. HAmAmsA I 'ATTORNEYS June 23, 1970 TUTOMU HANAFUSA 3,517,356

CIRCUIT INTERRUPTER 7 Sheets-Sheet 5 Filed July 24, 1968 EOS .my n

FIGB

INVENTOR TUTOMU HANAFUSA ATTORNEYS TUTOMU HANAFUSA 3,517,356

CIRCUIT INTERRUPTER 7 Sheets-Sheet 4 INVENTOR TUTOMU HANAFUSA ATTORNEYS June 23, 1970 Filed July 24, 1968 June 23, 1970 TUTOMU HANAFUSA 3,517,356

CIRCUIT INTERRUPTER Filed July 24, 1968 7 Sheets-Sheet 5 INVENTOR TUTQMU HANAFUSA ATTORNEYS June 23, 1970 TUTOMU HANAFUSA 3,517,356

.l CIRCUIT INTERRUPTER Filed July 24, 1968 7 Sheets-Sheet 6 FIQ INVENTOR TUTOMU HANAFUSA ATTORNEYS June 23 1970 Tu'roMu HANAFUSA 3,517,356

CIRCUIT INTERRUPTER Filed July 24, 1968 7 Sheets-Sheet 7 TUTOMU HANAFUSA ATTORNEYS United States Patent O 3,517,356 CIRCUIT INTERRUPTER Tutomu Hanafusa, Osaka, Japan, assignor to Terasaki Denki Sangyo Kabushiki Kaisha, Osaka, Japan Filed July 24, 1968, Ser. No. 747,189 Claims priority, application Japan, `luly 24, 1967, 42/47,237, 42/47,238 Int. Cl. H01h 77/10 U.S. Cl. 335--16 1 Claim ABSTRACT OF THE DISCLOSURE In the closed position of the disclosed circuit interrupter, a first and a second movable contact unit are disposed in opposed parallel relation while a pair of movable contact arms forming each unit are aligned with each other. The pair of second aligned contact arms are connected through individual stationary conductors to terminals remote from them respectively with each conductor having one portion disposed in parallel to the second contact arm in its closed position. A flow of current through the each conductor is the same in direction as through the second contact arms but opposite in direction to through the first arms. The first contact arms are translated to their open position through a manually opening or tripping operation. iUpon the occurrence of a flow of shortcircuiting current each pair of first and second arms are rotated in the opposite directions through an electromagnetic repulsion developed between them to interrupt the current. As the second rotating arms approach the associated conductor, their rotation is aided by an electromagnetic attraction developed between them. A little later after the interruption a tripping electromagnet is operated to bring the first arms into their open position where they are aligned with each other or put in a straight line. The second arms returned back to their original positions as the repulsion is attenuated.

The invention relates to improvements in the current limiting type of circuit interrupters utilizing an electromagnetic repulsion developed between a pair of substantially parallel electric conductors due to a ilow of very excessive current therethrough in the opposite directions.

-It is an object of the invention to provide a novel circuit interrupter of current limiting type improved in capability to limit a current flowing therethrough upon the occurrence of any shortcircuit failure and decreased in arcing and interrupting times to increase the capability of interruption as compared with the conventional circuit interrupters of the type above described.

The invention accomplishes the above object by the provision of a circuit interrupter comprising a pair of movable contact units disposed in opposed parallel relationship in the closed position of the interrupter, switching means operatively coupled to one of the movable contact units for driving the one unit from its closed position into its open position and vice versa, the other contact unit having only the contact function, a source terminal, and a load terminal, said movable contact units responding to an electromagnetic repulsion developed therebetween upon the occurrence of a flow of very excessive current to be rotated in the opposite directions about their respective axes of rotation independently of the operation of the switching means thereby to interrupt the current, characterized in that the one contact unit includes a pair of movable contact arms having contacts at one end and pivotably mounted at the other ends while maintaining electrical connection therebetween, said pair of movable contact arms being bilaterally disposed in alignment with each other in the closed position of the ice interrupter, the other contact unit including a pair of movable contact arms having contacts at one end and pivotably mounted at the other ends, the last-mentioned contact arms being connected in circuits respectively with the source and load terminals and bilaterally disposed in alignment with each other in the closed position of the interrupter 'where the contact arms of the one unit bridge those of the other unit so that a current flow in each arm of one of the units is in the same direction as a current flow in the other arm of that unit but in the opposite direction to a current flow in each arm of the remaining unit, each pair of directly opposed contact arms responding to the electromagnetic repulsion to be rotated in the opposite directions about their other ends simultaneously with the rotational movement of the arms of the other unit thereby to simultaneously separate two pairs of the contacts from each other.

Preferably each pair of directly opposed contact arms may be disposed a longer distance from that terminal connected to one of those arms than the other pair and one stationary electrical conductor may connect each terminal to that contact arm remote from the each terminal and have one portion disposed in parallel relationship with the associated contact arm such that the said portion is identical in a direction of current flow to the latter arm. Upon the occurrence of a flow of very cX- cessive current an electromagnetic attraction is developed between the said portion of the conductor and the associated movable Contact arm to increase a speed at which the said arm is being separated from the mating moving contact arm.

The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. l is an elevational sectional view of a three poled circuit interrupter constructed in accordance with the principles of the invention and put in its closed position;

FIG. 2 is a plan view of the interrupter as viewed from its bottom with a common cover for arc extinguishing chambers removed, with a first movable Contact unit for the central pole removed to illustrate a second contact unit and with a first and a second contact unit and arc extinguishing devices for another pole also omitted;

IFIG. 3 is a fragmental sectional View of the interrupter illustrating its open or reset position into which it is brought through the operation of the associated operating handle;

FIG. 4 is a fragmental sectional view of the interrupter illustrating its tripped position into which it is brought through the actuation of the associated trip device upon a ilow of ordinary overload current therethrough;

FIG. 5 is a fragmental sectional view of the interrupter illustrating its interruption position into which it is brought through a flow of shortcircuiting current therethrough and independently of the operation of the associated switching and trip devices;

FIG. 6 is a perspective view of the iirst and second movable contact units and the associated stationary conductors to form a closed loop circuit; and

FIG. 7 is a fragmental exploded perspective view of the essential parts of the interrupter.

While the invention will be illustrated and described in conjunction with a circuit interrupter of three pole type, it is to -be understood that the same is equally applicable to circuit interrupters of single pole ty-pe and other multiple pole types. Also it is to be understood that the components in common to al1 the poles will be described in terms of the central pole alone.

Referring now to the drawings and more particularly to FIG. 1, there is illustrated a three poled circuit interrupted constructed in accordance with the principles of the invention. The circuit interrupter illustrated comprises a closed enclosure including a main body member 1, a detachable top cover member 2, and a detachable bottom cover member 3. All the members 1, 2 and 3 may be conveniently made of any suitable, electrically insulating plastic by the molding technique. Within the enclosure a pair of movable contact units generally designated by the reference numerals 4 and 5 respectively are disposed so as to be substantially horizontally positioned in opposed parallel relationship in the closed position of the interrupter.

A first or lower one of both units 4 includes a pair of first or lower contact arms 4s and l having a pair of contacts 6s and l attached to the extremities or free ends respectively. The contact arms 4s and l may be conveniently made of any suitable electrically conductive material. Both contact arms 6s and l are of a ibilaterally symmetric configuration excepting that one of them in this case arm 4s has a projection 7s of partially circular section at the other end while the other contact arm 4l has a V-shaped groove 7l formed at the adjacent end. Both arms are bilaterally disposed in alignment with each other in the closed position of the interrupter. The projection 7s is then forced always to engage the groove 7l under a pressure by the action of two tension springs 8 (see also FIG. 2) on both sides of the arms 4s and l spanned between a pair of anchoring pins 9s and l rigidly extending through the respective arms. Then the contact arm 4s is mounted at the center of the projection 7s on a pivot pin 10 rotatably carried by a pair of spaced contact holder 11 and 11 and therebetween. Thus the first contact arm 4s is arranged to be rotatable about the axis of the pin 10 while the contact arm 4l is rotatable about the axis of the pin 10 With the circularly arcuate surface of the projection 7s kept in Contact with the V-shaped groove 7l. However it is noted that in the closed position of the interrupter those sides facing the upper contact unit 5 of the contact arms 4s and I and therefore the first contacts 6s and l are substantially flush with each other. To ensure the electrical connection the contact arm 4s is electrically connected to the contact arm 4l. A flexible shunting lead 12 is connected between the adjacent end portions thereof as shown in FIG. 1.

The second or upper contact unit 5 includes a pair of second or upper Contact arms 5s and l of bilaterally symmetrical configuration spaced away from each other and having a pair of contacts 13s and l attached to their free ends or extremities respectively. The upper contact arms may be conveniently made of the same metallic material as the lower contact arms. In the closed position of the interrupter, those sides facing the first contact arms of the second contact arms 5s and l are substantially flush with each other and bridged by the lfirst contact unit 4 by having the contacts 13s and l engaged by the respective contacts 6s and l. The upper contact arms 5s and l are pivotably mounted at the other ends on pivot pins 14s and l respectively.

As best shown in FIG. 2, the pivot pins 14s and l are rigidly secured to a pair of opposed holding frames 15s and l which are, in turn, mounted to the main enclosure body 1 through the respective screws 16s and l. Spanned between an anchoring pin 17s rigidly extending through the substantially middle portion of the contact arm `5s and a stop pin 18s fixed on the holding frame 15s on both side of the contact arm for the purpose of imparting to the contact 13s a pressure under which it is in engagement with the mating contact 6s. For the same purpose the Contact arm 5l is operatively associated with the corresponding components 171, L81 and 191. The tension springs 8 operatively coupled to the lower contact arms 4s and l also aid to provide contact pressures for the contacts 6s and l. It is noted that the second Contact unit 5 has only the contact function.

As shown in FIGS. 1 and 6, the upper Contact arm 5s is electrically connected through a fiexible lead 20s to a connecting element 21s welded to one end of a stationary electric conductor 22s. Th conductor 22s is embedded in an electrically insulating partition 1a for physically separating the contact units 4 and 5 from a switching mechanism as will be described hereinafter and is connected to a source terminal 23s disposed on one edge of the main enclosure body 1. Similarly the upper contact arm 5l is electrically connected through a flexible lead 20], a connecting element Zll and another stationary electric conductor 221 to a load terminal 231 disposed in opposite relationship with the source terminal 23s and on the opposite side of the main body 1. Thus it is noted that each pair of first and second movable contact arms 4s and 5s or `4l or 5l are disposed a longer distance from the terminal 23s or l connected thereto than from the other terminal within the enclosure of the interrupter. As shown in FIG. 6, both conductors 22s and l are of a symmetrical configuration and each of them includes one portions 22s or l located substantially in parallel to all the contact arms in closed position of the interrupter and horizontally superposing each other.

As shown in FIG. 1, the circuit interrupter further includes a pair of opposed arc extinguishing chambers 24s and l of the conventional construction adjacent to the free end portions of the upper and lower contact arms. Therefore the bottom `cover member 3 also serves as a common cover for the chambers.

In order to manually open and close the circuit interrupter, that is to say, to manually move the lower contact unit 4 away and toward the upper contact unit 5, there is a switching mechanism generally designated by the reference numeral 25. The switching mechanism 25 cornprises a pivotable operating handle 26 having one end portion loosely projecting beyond the top cover member 2, and a switching lever 27 of inverted U-shape secured to the operating handle 26 at the other end. Then the lever 27 is pivotably mounted at the free or other end on a pivot pin 28 planted on support plates 29 suitably disposed on the main enclosure body 1. Thus the operating handle 26 and the switching lever 27 as a whole are adapted to be turnable about the axis of the pin 28. The mechanism further comprises a pair of toggle elements 30 and 31 articulated at a pin 32 to eac-h other with the free end of the toggle element 31 pivotably mounted on a pivot pin 33 secured to one end of a contact lever 34. A pair of tension springs 35 on each side of the switching lever 27 `are anchored at one end to the switching lever 27 and at the other ends to the toggle -pin 32. The contact lever 34 is pivotably mounted on the pivot pin 28 and has extending through the other end an interlocking switching shaft 36.

Fitted onto the interlocking switching shaft 36 are three pairs of spaced contact holders 11 and 11 at the upper ends in spaced parallel relationship one pair for each pole as shown in FIG. 7. The contact holder 11 or 11 for each pole is made preferably of any suitable reinforced synthetic plastic high in mechanical strength, and loosely extends through a vertical complemental opening 1c or c bored throughout a central post 1b formed integrally with the main enclosure body 1 (see FIGS. 2 and 7). The lower portions of the two contact holders 11 and 11' projecting beyond the opening 1c and c' is enlarged in width and have centrally extending at the lower ends a retaining pin 37 provided at each end with a guide roller 38 adapted to roll along a guide groove 3a formed on each of the common side walls of the arc extinguishing chambers 24s and l for the purpose as will be apparent hereinafter. The first or lower movable contact unit or the two lower movable contact arms 4s and l is or are sandwiched fbetween the lower wider portions of the two mating contact holders 11 and 11 and above the retaining pin 37 for rotational movement about the axis of the pivot pin 10. As best shown in FIG. 7, the mating contact holders are provided on both sides of the lower end portion with a pair of bilateral recesses 39s and l along which are guided the anchoring pins 9s and l on the respective lower contact arms 4s and l.

For a tripping operation, there is provided a trip mechanism generally designated by the reference numeral 40. The trip mechanism 40 may be of the conventional construction and in the embodiment illustrated comprises a trip lever 41 pivotably mounted at one end on a pivot pin 42 bridging the two parallel support plates 29 as previously described and provided on the central portion with a toggle pin 43 on which, the free end of the toggle element 30 is pivotably mounted. The trip lever 41 is normally engaged at the other end by a trip hook 44 pivotably mounted on a hook pin 44C supported by the support plates 29. The trip hook 44 has one end portion 44a shaped into a grooved edge normally engaging the trip lever 41 and the other end 44b serving to receive a trip piece 45 secured on an interlocking trip shaft 46. The trip shaft 46 is pivotably supported by the support plates 29 and further includes a trip piece similar to the piece 45 just described for each of the remaining poles except for a shoulder 45a disposed on the piece for the central pole to normally engage the trip hook 44.

Further the circuit interrupter comprises a thermally responsive mechanism and an electromagnetically responsive mechanism each of which may be of the conventional construction.

The thermally responsive mechanism generally designated by the reference numeral 50 comprises a bimetallic element 51 and an electric resistance type heater 52. The bimetallic element and heater 51 and 52 respectively are along with an energizing winding for an electromagnet as will be described hereinafter are connected at one end in superposed relationship to a supporting bracket 53 rigidly secured to the main enclosure body 1. The bimetallic element 51 has the other or free end facing a trip adjusting screw 54 thread screwed into the other end of the trip piece 45 while the heater 52 is connected at the other end to a heaters terminal 55 which is, in turn, connected to the stationary conductor 221 on the load side.

The electromagnetically responsive mechanism generally designated by the reference numeral 56 includes an electromagnet comprising a stationary iron core 57 having a cylindrical leg portion 57a, an energizing winding 57b inductively disposed on the leg portion 57a and a pair of spaced pole pieces 57C secured at both ends of the leg portion. The stationary core 57 is suitably secured to the support plates 29 While the winding 5717 is connected at one end to both the heater and bimetallic element 51 and 52 respectively in the manner as above described and at the other end to the load terminal 23! through an electric conductor 58.

The electromagnetically responsive mechanism 56 further comprises an instantaneously tripping lever 59 pivotably mounted on the central portion to the support plates 29. The lever 59 includes three arms 59m, b and c one of which 59a has a movable iron core 60 attached to the extremity so as to be positioned in slightly spaced, opposite relationship with the pole pieces 57e of the stationary core. The second arm 59b faces a pin 61 disposed at the other end of the trip piece 45 and the third arm c extending between the arm 59a and b has attached to its extremity an indication plate 62 viewable through an indication window 2a formed on the top cover member 2. The indication plate 62 serves to indicate the operation of the instantaneously responsive mechanism 56. A tripping spring 63 is spanned between the support plate 29 and the third arm 59C and tends to rotate the tripping lever 59 in the counterclockwise direction as viewed in FIG. 1 until the movable iron core 60 is biased to abut against an eccentric cam 64.

In order to adjust current owing the interrupter to a magnitude suflicient to trip the interrupter, a current controlling screw 65 rotatably projects beyond a through hole 2b formed on the top cover member 2 and has the eccentric cam 64 secured on the lower end portion. The rotational movement of the controlling screw 65 causes the movable iron core 60 to be forcably rotated to change a gap between the movable and stationary iron cores for the purpose of controlling the magnitude of the tripping current.

The circuit interrupter thus far described is operated as follows: In FIG. l wherein the interrupter is illustrated in its closed position, the operating handle 26 can be manually turned to the OFF side to canse the toggle elements 30 and 31 to collapse thereby to cause the contact lever 34 to be rotated about the axis of the pin 28 in the clockwise direction as viewed in FIG. 1. This rotational movement of the contact lever 34 is accompanied by the downward movement of the contact holders 11 and 11 to permit the lower contact arms 4s and l to be separated from the upper contact arms 5s and l and while the lower arms are maintained in a horizontal straight line as in their closed position until the lower contact arms are brought into their positions as illustrated in FIG. 3. That is the lower contact arms 4s and l are translated to their open position. It will be appreciated that the guide rollers 38 on the holding pin 37 slide downwardly along the associated guide grooves 3a on the opposite insulating side walls of the arc extinguishing chambers 24s and l to ensure that the lower contacts are smoothly and rapidly separated away from the upper contacts. j

If it is desired to close the open interrupter, the operating handle 26 can be manually turned to the ON side to cause the process reversed from that as above described to proceed until the lower contacts 6s and l are put and maintained in engagement with the upper contacts 13s and l respectively.

With an ordinary overload current flowing through the circuit interrupter in its closed position, the bimetallic element 51 is heated to deect until its free end pushes against the trip adjusting screw 54. This causes both the trip piece 45 and the interlocking trip shaft 46 to be rotated in the counterclockwise direction as viewed in FIG. 1 whereby the trip piece 45 disengages from the trip hook 44 resulting in the rotational movement of the trip hook 44 in the counterclockwise direction. This causes the trip lever 41 to disengage from the trip hook 44 whereupon the toggle elements 30 and 31 collapse. Thereafter the process as above described in terms of the manually operation, is repeated until the interrupter is brought into its tripped position as illustrated in FIG. 4.

If an excessive current whose magnitude is equal to from ve to ten times the rating current for the interrupter in its closed position flows through the latter, the movable iron core 60 is immediately attracted to the stationary iron core 57 to rotate the instantaneously tripping lever 59 until the trip responsive pin 61 on the trip piece 45 is raised. This raising of the piece 45 causes the process as above described in conjunction with the deilection of the bimetallic element 51 to be repeated until the interrupter is similarly brought into its tripped position.

If a very excessive current such as a shortcircuiting current ows through the interrupter in its closed position, the current flows in the opposite directions through second contact arms 5s and 5l and the iirst contact arms 4s, 4l to develop an electromagnetic repulsion serves to rotate immediately the iirst or lower contact arms 4s and l in the opposite directions about the axis of the pivot pin 10 while the V-shaped groove 7l on the arm 4l slides along the periphery of the projection 7s on the arm 4s. At the same time the second or upper contact arms 5s and l are rotated in the opposite directions about the axes of the respective pins 14s and l. Thus, the contacts 6s and 13s are rapidly separated in the opposite directions from each other as do the contacts 6l and 13l whereby the shortcircuiting current is interrupted.

It is to be noted that the contact arms effect the respective rotational movement independently of the operation of the trip mechanism 40 as above described and without any time delay due to the construction while the contact holders l1 and l1 are maintained in their original position as illustrated in FIG. 1.

The rotational movement of both iirst contact arms 4s and l in the opposite directions is accompanied by the displacement of the anchoring pins 9s and l thereon leading to the reversion of the action of the contact springs 8 to fold the contact arms `4s and l. Finally the contact arms 4s and l abut against Stoppers 3a formed on the bottom cover member 3 to be maintained folded into the inverted V-shape. On the other hand, the upper contact arms s and l are similarly folded into V-shape and maintained in that shape as long as the electromagnetic repulsion exceeds the force of the contact springs 19s and l for maintaining the contact arms in the V-shape or in their open position. IFIG. 5 shows the upper and lower contact arms in their interruption positions. However as the repulsion is attenuated the upper Contact arms are returned back to their original closed position while the lower contact arms are in their interruption.

It is to be understood that the contact springs 19s and l may readily be designed and arranged so as to reverse in the action thereof during the rotational movement of the second contact arms which comes into the scope of the invention.

A little later after the first and second contact units 4 and 5 and therefore the first contacts 6 and 9 has been separated from each other thereby to interrupt the shortcircuiting current, the electromagnetically responsive mechanism 56 is operated to overide the ability of the switching mechanism 25 through the trip mechanism 40. That is, the toggle elements 30 and 31 are released from their constraint to depress the interlocking switching shaft 36 and hence the contact holders 11 and 11 whereby the abutting end portions of the rst contact arms 4s and l folded in inverted V-shape are forced downwardly. Therefore these Contact arms are permitted to be rotated upwardly as viewed in FIG. 1 about the axis of the pivot pin l0. During this rotational movement, the contact springs 8 reverses in its direction of action to horizontally align the contact arms 4s and l with each other as in their closed position. Then the interrpter is required only to be reset to be ready for the succeeding closing operation as do the conventional interrupters.

Due to the fact that, as previously described, a pair of first movable contact arms 4s and l and a pair of second movable contact arms 5s and l are disposed in opposite parallel relationship in the closed position of the circuit interrupter and that each pair of mating contacts 6s and 13s or 6l and 13! attached to the free ends of directly opposed contact arms are adapted torespond to an electromagnetic repulsion developed between the associated opposed arms through a flowof very excessive current therethrough to be moved away from each other simultaneously with the similar movement of the other Contact pair, a distance of separation between the mating contacts can increase easily enough. This leads to the advantages that the present circuit interrupter of current limiting type having two interruption points is increased in current limiting capability to such an extent that the interrupter nearly resembles in operation the four interruption point type of interrupters and the arcing time as well as the entire interruption time decreases leading to an increase in interruption capability.

In the conventional current limiting type of low voltage circuit interrupters operative with a low rating current such as 100 amperes, it has been difficult to impart to the interrupters a normal interruption capability as high as 100,000 amperes at 500 volts of AC voltage. However, the circuit interrupter of the invention even though similar in size to the cited interrupters, posseses a high interruption capability such as above specied while it completes an interruption time within twenty percent of one cycle of alternating current or less.

Further the present interrupter is not at all inferior in interruption capability to any current limiting fuse presently used and rather somewhat gentle and low in arcing voltage as compared with the fuse steep and high in arcing voltage. This results in a decrease in fear that the associated electric devices may be broken down.

As previously described, each of the source and load terminals 23s or l is electrically connected to the upper movable movable contact arm 5s or l disposed a longer distance from the same than from the other terminal through the individual stationary conductor 22s or l including one portion disposed in substantially parallel relationship with the contact arms `5s and 4s or `5l and 4l in their closed positions. A ow of current through each conductor is the same in direction as through the upper contact arms but opposite in direction to through the lower contact arms. Upon separating two pairs of contacts in response to a very excessive ilowing through the contact arms, the upper contact arms 5s and l are rotated about the aXes of the respective pivot pins 14s and l to approach the associated conductor 22s or l. This rotational movement of both contact arms is accompanied by the generation of an electromagnetic attraction between each of the upper contact arms and the connector connected thereto resulting from a flow of current therethrough in a common direction as shown at the arrows in FIG. 6. This aids in separating the upper contact arms `Ss and l from the associated lower Contact arms 4s and l thereby to increase a speed at which the contact arms 5s and l are being separated away from the contact arms `4s and l respectively with the result that the current limiting capability additionally increases.

While the invention has been illustrated and described in conjunction with a single preferred embodiment thereof it is to be understood that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.

What I claim is:

1. In a circuit interrupter comprising a pair of movable contact arm units disposed in opposed parallel relationship in the closed position of the interrupter, switching means operatively coupled to one of said movable contact units for driving said one unit from its closed position into its open position and vice versa, the other movable contact arm unit having only the contact function, a source terminal, and a load terminal, said movable Contact arm units responding to an electromagnetic repulsion developed therebetween upon the occurrence of a ow of very excessive current to be rotated in the opposite directions about their respective axes of rotation independently of the operation of said switching means thereby to interrupt the current, said one contact arm unit including a pair of movable contact arms having contacts at one end and pivotably mounted at the other ends while maintaining electrical connection therebetween, said pair of movable contact arms being bilaterally disposed in alignment with each other in the closed position Iof said interrupter, the other contact arm unit including a pair of movable contact arms having contacts at one end and pivotably mounted at the other ends, said last-mentioned contact arms being connected in circuits respectively with the source and load terminals and bilaterally disposed in alignment with each other in the closed position of the interrupter where said contact arms of said one unit bridge those of the other unit so that a current flow in each arm of one unit is in the same direction as a current ow in the other arm of that unit but in the opposite direction to a current ow in each arm of the other unit, each pair of directly opposed contact arms responding to said electromagnetic repulsion to be rotated in the opposite directions about their other ends simultaneously with the rotational movement of the arms of the other unit thereby to simultaneously separate the two pairs of said contact from each other, and one stationary electric conductor for electrically connecting each of said movable contact arms of said other unit to the associated terminals and having one portion disposed in parallel relationship with the connected contact arms and identical in a direction of current flow to that contact arm connected thereto so that upon the occurrence of very excessive current, an electromagnetic attraction is developed between said portion of each conductor and the associated movable contact arm of said other unit to increase a speed at which that contact arm is being separated from the mating Contact arm of said one unit.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner 

